1. Technical Field
The present invention relates to an optical recording device and to an optical recording method.
2. Related Art
Coaxial recording methods (collinear methods) have recently been proposed as holographic memory recording and reproduction methods. Collinear methods have advantages, in comparison to conventional twin beam interference methods, such as dramatically simplifying the optical system used, being robust to external disturbances like vibrations, and servo mechanisms being readily introduced thereto. In collinear methods light of a signal beam and a reference beam having the same optical axis is converged by a common lens. However, the region in which a hologram is formed thereby is limited to a range within the very close vicinity of the focal plane, since interference is induce using the common lens. This means that the dynamic range (multiplicity) of a thick layer medium cannot be effectively utilized.
However, a conventional collinear method can only form a single three-dimensional hologram in the layer thickness direction of the medium. Therefore, it is necessary to make a small separation distance between adjacent holograms in the in-plane direction, in order to raise the recording density by shift multi-recording. This method tends to reduce the recording sensitivity as the multiplicity is increased, cross-talk is also increased between adjacent holograms and this inhibits increases in the capacity of optical recording media.